Conventionally, a multi-tone (i.e., continuous tone) original image has been halftoned using a threshold matrix and recorded on a recording medium. As one example of the threshold matrix generation methods, such a method as disclosed in Japanese Patent Application Laid-Open No. 2008-294702 is known, in which an evaluation value is obtained based on the distance between each target pixel and the previously turned-on pixel so that the pixel that is subsequently turned on is as distant as possible from the previously turned-on pixel, and a turn-on order is determined based on the evaluation values.
Incidentally, in the case of recording images using a threshold matrix generated by the method as disclosed in Japanese Patent Application Laid-Open No. 2008-294702, areas where dots are disposed in a grid may appear in a specific tonal range. Such grid-like dot areas will feel unnatural to viewers of images when compared with areas where dots are randomly disposed.